A disadvantage of unsaturated polyester resins, hereinafter called UP, which have many industrially desirable properties, is the considerable shrinkage of these plastics upon curing, however; it may amount to up to 60 to 10% and may still be considerable even when fiber fillings, in particular glass fibers, are added. If shrinkage of the UP resins in cross-linking is to be avoided, it is necessary as a rule to use fillers, yet they are often undesirable for other reasons or can cause difficulties in industrial processing. Epoxy resins, hereinafter called EP, have the same disadvantages.
Laminate plastics for tubes, for instance, have therefore so far required a relatively complicated production process, since as a rule the inner layer is embodied as a so-called liner, which must be mounted on a mandrel and then provided with the jacket layer wound on its outside. In cross-linking of the jacket layer, which was previously typically done thermally, shrinkage occurs, however, which can in turn lead to hairline cracks in the liner. The production of such tubes therefore requires not only a great deal of experience, but is also time-consuming and expensive, and this makes itself felt in the relatively high prices for the finished products. Instead of the usual thermal cross-linking of the outer layer, cold curing of such synthetic resins is already known, but that has the disadvantage in turn that the UP resin, provided with hardeners and accelerators, allows only very brief processing times of the starting mixture. EP resins can also be processed by cold curing; however, the curing time is longer than with UP resins.
There is accordingly a need for practically shrinkage-free laminate plastics of thermal plastics for the inner and reaction resins for the outer layer that can be produced in a relatively economical process.